Preparation, structural and optical properties of a new class of compounds, Bi2MNbO7 (M=Al, Ga, In)

A new class of compounds, Bi2MNbO7 (M=Al, Ga, In), were synthesized by the solid-state reaction and characterized by powder X-ray diffraction and Rietveld structure refinement. The optical absorption and structural properties of Bi2MNbO7 (M=Al, Ga, In) were investigated. These compounds crystallize in the same pyrochlore structure, but the lattice parameters decrease with decreasing M (M=Al, Ga, In) ionic radii. The band gaps of the Bi2MNbO7 (M=Al, Ga, In) compounds were estimated to be about 2.9, 2.75 and 2.7 eV, respectively.